Here are some steps how to install an ESXi host from a USB key. If you have a host that does not have a CD drive or if you have a stubborn USB key that does not want to boot from an ESXi image. Follow these steps to clean the USB disk and then copy the image onto it to make it bootable.
1. Run DISKPART to clean up and prepare the USB
2. Use “Unetbootin” to install the ESXi iso onto the USB key